The present invention pertains to enclosures for housing gas cylinders, distribution piping and manifolds used to store, distribute and dispense hazardous materials, such enclosures being generally referred to in the industry as gas cabinets, valve manifold boxes (VMB) and gas isolation boxes (GIB).
In the manufacture of semi-conductor devices, hazardous materials, such as gaseous silane are used. The gaseous materials are generally packaged in cylinders which are transported to the semi-conductor fabrication site (FAB) where the material is withdrawn and used to manufacture the semi-conductor devices. In order to protect the ambient environment, in the case of a leak in the distribution piping associated with withdrawing the gas from the cylinder, the cylinders are placed in a ventilated enclosure or gas cabinet. The gas cabinet contains all of the necessary piping and controls for selectively withdrawing the material from the cylinder and conducting it to a central pipeline for dispersion to the actual semi-conductor manufacturing operation or through a VMB or a GIB for redistribution in the FAB. Conventional gas cabinets have an inlet and outlet ducting so that ambient atmosphere can be continuously drawn through the cabinet and exhausted, thus sweeping into the exhaust system of the FAB any hazardous material leaking from the cylinder or the associated piping and controls.
Gas cabinets, valve manifold boxes and gas isolation boxes are widely available in industry. Numerous models are available from Air Products and Chemicals, Inc., Allentown, Pa.
U.S. Pat. No. 4,625,627 is illustrative of a ventilated gas cabinet for use in handling and dispensing hazardous gaseous materials.
U.S. Pat. Nos. 4,866,594; 4,989,160; 5,220,517; 5,497,316 and 5,508,947 further describe gas cabinets and methods for withdrawing the material contained in the cylinders and directing the material to a point of use.
One problem with known gas cabinets is that regulatory agencies are constantly changing the requirements for ambient atmosphere flow through the cabinets in order to have adequate ventilation of the cabinets. Most conventional gas cabinets are set up so that ambient atmosphere flows through the cabinet at the rate of about 50 to 100 feet per minute. Regulations have been made to require a minimum flow of 200 feet per minute inside of the cabinet especially in the vicinity of any non-soldered or non-welded pipe or fitting joint associated with the dispensing of a hazardous material. In order to achieve this type of flow in a conventional gas cabinet significantly increased capacity fans or blowers would be required for the users evacuation system. Merely increasing through velocity of the total volume of atmosphere would create significant problems for the user of the gas cabinet. Among these are higher capital costs, higher operating costs, such as energy requirements and maintenance, and additional space for equipment.